The morphogenetic assembly of cells into functional tissues involves specific cellular interactions mediated by the plasma membrane. The cellular slime mold Dictyostelium discoideum provides an exciting model system in which to study the molecular basis of cell recognition during development. The objective of the proposed research is to elucidate the role of an endogenous lectin called Carbohydrate Binding Protein (CBP) in morphogenetic cell cohesion. The focal point for these studies is the discovery of an unusual structure for localized at the cell surface: it appears to be a glycosylated dimer of identical monomers, stable to denaturation in the presence of reducing agents. Experiments will be directed towards the following questions: (1) What is the nature of the interchain bonds in the CBP dimer, and what is the enzymatic mechanism of their formation?, (2) the dimer formed by binding of monomers on the same cell or between opposing cells?, What are the kinetic relationships between glycosylation of CBP, transmembrane insert and dimer formation?, and (4) What is the significance of the surface-localized dimer for morphogenetic cell cohesion?